border-1px($color)
  position : relative
  &:after
    display : block
    position : absolute
    left : 0
    bottom : 0
    width : 100%
    border-top : 1px solid $color
    content : ' '
border-none()
  &:after
    display none
bg-image($url)
  background-image:url($url+ "@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
    background-image: url($url+ "@3x.png")
